RPM spike/ sticking

Maintenance/Repairs
1

1987 Ford F150 v8 5.0 302 automatic 123k miles

I had a similar problem a while back with this truck. After driving any distance and putting it in park, the RPMs will Spike to about 2000. A quick kick on the gas pedal will knock it back down to normal. It also happens when driving through town (35 mph or so). It was happening really harshly before and causing it to stall. This time, it just feels like I’m fighting acceleration. The mechanic ended up unplugging the IAC valve (when he unplugged it, the rpm dropped to normal, replugged and it would spike) and it’s been driving well since, up to the last few days. I had replaced the TPS around the time he did the IAC unplugging. The throttle body is clean, I make sure it doesn’t go too long without being sprayed and wipes down (did so yesterday to be thorough) and even sprayed the springs around the top of the throttle.

I’ve researched the issue and can’t find exactly what I’m experiencing, where blipping the accelerator normalizes the RPMs. I’ve gotten the same spiking rpm with and without the IAC valve plugged in, but it still runs and idles better with it unplugged

2

I have a wild guess. Assuming this car has a carb, I would guess that the carb linkage is dirty and
sticking.

3

Not sure how many threads you have on this vehicle but they seem to go back to August 2018.
Don’t you think it is time to have a professional shop solve this ?

4

No carburetor in it, fuel injection.

It’s the second post about it, with the problem having been gone for months and a similar issue now occurring.

The idle doesn’t fluctuate up and down. When placed in park, the RPMs just go up to approximately 2000 and stay there. No surging going on when parked or driving

5

Replace the IAC, clean the throttle body, check the throttle body for a worn shaft and housing.

1 Like
6

I went ahead and ordered a new IAC valve. This morning when I started it, I let it run for a minute then plugged the IAC connector into the IAC valve and it stalled immediately

7

Tells me you have a vacuum leak.

tells me you still have a vacuum leak.

8

Would that cause 0 deceleration after taking my foot off the accelerator? And cause me to have to kick and release the gas pedal to lower the speed and RPM?